The present invention pertains to the field of polymers containing active azo moieties and monomers for making those polymers.
Graft and block copolymers are copolymers wherein specific areas of the polymer contain different combinations of mer units. For instance, in a graft polymer a polymer backbone comprising one combination of mer units is attached to polymer branches which consist of a different combination of mer units. Such graft copolymers are conveniently made by forming a polymer backbone with initiator sites that may be used to initiate polymerization in a different monomer composition. Organic azo compounds are known to initiate free radicals at the site of the azo group through thermally, photolytically and chemically induced decomposition of the azo group.
Kerber et al. demonstrated that .alpha.,.alpha.-dicyanoethylazostyrene could be copolymerized with styrene at temperatures of about 0.degree. C. to 60.degree. C. to form a polystyrene backbone with pendant dicyanoethylazo moieties. The azo group could subsequently be decomposed by temperatures of about 70.degree. C. or more to initiate polymerization in vinylic monomers. Kerber et al., Synthese und Charakterisierung von Copolymeren aus Azo-Initiatoren und Styrol, 177 Macromolecular Chem. 1357-1371 (1976): Kerber et al., Propfung und Vernetzung mittels Azogruppen enthaltender Copolymerer6, 178 Macromolecular Chem. 1833 (1977): Kerber et al., Uber die Copolymerisation von (3-Vinylphenylazo)-methyl-malonodinitril mit Styrol, 179 Macromolecular Chem. 1803 (1978); Kerber et al., Azoinitiatorn,9)Synthese und Pfropfung azogruppenhaltiger Polycarbonate, 180 Macromolecular Chem. 609 (1979).
The cyanoethyl-azo-styrene monomers and polymers of Kerber et al. share several problems which decrease their commercial utility. The azo group in the Kerber monomers and polymers is highly temperature sensitive and decomposes swiftly even at low temperatures of about 70.degree. C. The polymer is unstable for extended shelf-life. Furthermore, the polymer cannot be formed or purified by processes which proceed at temperatures in excess of 70.degree. C.
What is needed is a polymer containing pendant azo moieties which can be produced and processed at relatively high temperatures, which can be stored indefinitely at room temperature, and which can be easily activated to initiate polymerization at temperatures below that which causes thermal degradation of the polymer.